Non-Preemptive Real-Time Multiprocessor Scheduling Beyond Work-Conserving

Abstract

Although essential for Inherently non-preemptive tasks and favorable to tasks with large preemption/migration overheads, non-preemptive scheduling has not been thoroughly studied compared to preemptive scheduling. In particular, existing studies for non-preemptive scheduling could not effectively exploit being non-work-conserving (i.e., idling processor(s) intentionally), failing to achieve its full schedulability capability. In this paper, we propose the first non-preemptive scheduling framework that covers work-conserving-infeasible task sets (each of which is proven unschedulable by every work-conserving non-preemptive scheduling), without knowledge of future release patterns of tasks (i.e., without clairvoyance). To this end, we first discover the following principle: without clairvoyance, it is impossible to generate a feasible schedule for work-conserving-infeasible task sets on a uniprocessor platform. To make it possible on a multi-processor platform, we design the NWC(N)-NP-* framework that systematically idles up to N processors so as to enable N designated tasks (that yield work-conserving-infeasibility) to be schedulable without clairvoyance, and derive important properties of the framework. We then target the framework associated with fixed- priority scheduling (as a prioritization policy), and develop its schedulability test by utilizing the framework's properties. Our simulation results demonstrate that the proposed framework successfully covers a number of work-conserving-infeasible task sets, none of which can be deemed schedulable by any previous approach.